A CMOS image sensor is a device which may covert optical images into electrical signals using machine vision. A CMOS image sensor may include a pixel region which responds to the optical signals and a periphery region that does not respond to optical signals. A pixel region may generate electricity through photoelectric effect in response to light.
A silicide process may be performed when a CMOS image sensor is manufactured. In a silicide process, metal may be diffused into a silicon substrate to lower the resistance. A silicide process may be used to maintain relatively high performance of a device. Silicide may be formed regions outside a pixel region. Silicide formed in a pixel region may degrade electrical characteristics of a device by lowering light transmittance and causing junction leakage.
A plug (e.g. a conductive plug) may connect to a photodiode in the pixel region. A silicide process may not be performed with relation to the plug. Accordingly, a plug may not have silicide formed on it. A plug may receive a portion of the light irradiated onto the pixel region, which may generate some electrons from a photoelectric effect. As a result, electrons generated by the plug may cause undesirable electrical signals (e.g. noise) in an image sensor, which may compromise performance and reliability of an image sensor.